However, they’re not kept indefinitely. Messages are typically saved for three to seven days, depending on your plan. If you need to keep a longer record of your messages, you can use an app like SMS Backup & Restore to back them up to your computer or another device.
How to Use the Built-In DIGITS App | T-Mobile
How can I read my text messages online tmobile?
Does T-Mobile save text message content?
There is no definitive answer to this question since it depends on the phone and texting app you are using. Generally speaking, however, deleted texts are not actually gone forever. Instead, they are usually just hidden from view on your phone. This means that if you want to retrieve a deleted text, it is usually possible to do so with the right tools.
Many people like to have hard copies of their phone records, whether it's for personal reasons or to have records on file for business purposes.
Prepaid
If you have access to a computer, a printer, and a postpaid account, you can print up to one year of your phone records through T-Mobile.com.